That repo seems to have been created less than an hour ago.
Give Google a little time to parse the new repos, and it should show up.
Note that it is referenced by GitHub search already:
https://github.com/search?utf8=%E2%9C%93&q=RoboSpice-Extn-Retrofit-Tutorial
As the OP used the Webmaster Tools to submit its url, the repo is now indexed in Google.
Update 2019: the section "Enabling GitHub Pages to publish your site from master or gh-pages" is now (since 2014) more precise:
To select master
or gh-pages
as your publishing source, you must have the branch present in your repository.
If you don't have a master
or gh-pages
branch, you can create them and then return to source settings to change your publishing source.
Once the correct branch is created/populated, and selected as the publishing source, the Google indexing seems to be very quick.